Progressive and self-limiting neurodegenerative disorders in Africa: a new prominent field of research led by South Africa but without strong health policy

Introduction Neurodegenerative disorders are involved in mortality and morbidity of every country. A high prevalence is estimated in Africa. Neurodegenerative disorders are defined by a progressive or self-limiting alteration of neurons implied in specific functional and anatomical functions. It encompasses a various range of clinical disorders from self-limiting to progressive. Focus on public health policies and scientific research is needed to understand the mechanisms to reduce this high prevalence. We use bibliometrics and mapping tools to explore the area studies and countries involved in scientific research on neurodegenerative disorders in Africa. Methods We used two databases: Web of Science and Pubmed. We analyzed the journals, most cited articles, authors, publication years, organizations, funding agencies, countries and keywords in Web of Science Core collection database and publication years and Medical Subject Headings in Pubmed database. We mapped the data using VOSviewer. Results We accessed 44 articles published between 1975 and 2014 in Web of Science Core collection Database and 669 from Pubmed database. The majority of which were after 2006. The main countries involved in research on neurodegenerative disorders in Africa the USA, the United Kingdom, France and South Africa representing the main network collaboration. Clinical neurology and Genetics hereditary are the main Web of Science categories whereas Neurosciences and Biochemistry and Molecular Biology are the main Web of Science categories for the general search “neurodegenerative disorders” not restrained to Africa. This is confirmed by Medical Subject Headings analysis from Pubmed with one more area study: Treatment. Conclusion Neurodegenerative disorders research is leaded by South Africa with a network involving the USA, the UK, as well as African countries such Zambia. The chief field that emerged was on patient and hereditary as well as treatment. Public health policies were lacking fields in research whereas prevalence is estimated to be important in every country. New 17 sustainable development goals of the United Nations could help in this way.


Introduction
Neurodegenerative disorders (ND) encompass various pathologies from well-identified genetic abnormalities such as Huntington's disease [1] to multifactorial mechanisms such as Parkinson disease or Alzheimer disease [2][3]. ND are characterized by a progressive dysfunction of the central nervous system. Definitions of neurodegeneration can be multiple and we define it in this paper as a progressive or self-limiting alteration of neurons implied in specific functional and anatomical functions [4]. Nevertheless, clinical findings of ND are not only neurologic and can also be multisystemic, it means with dysfunctions of other organs such as in Huntington's disease [5]. Prevalence of neurodegenerative disorders is very high. For example, in Europe, only Parkinson disease is estimated from 65.6 per 100,000 to 12,500 per 100,000 inhabitants [6]. Costs are huge; estimation in 2004 in Europe is 386 billion euros [7]. Neurodegenerative disorders are involved in mortality and morbidity of every country. A high prevalence is estimated in Africa [8]. Focus on public health policies and scientific research is needed to understand the mechanisms to reduce this prevalence. In order to focus on a Africa-relevant approach, I will study both progressive and self-limiting neurodegenerative disorders, including, for example Nodding Syndrome (progressive) and cassavism, lathyrism (selflimiting). All of these disorders have been and are likely to continue to be endemic/epidemic regionally in Africa [9][10]. The aim of this article is to analyze scientific publications on neurodegenerative disorders in Africa and to determine the links between the countries involved and the area studies.

Methods
We used previously described methods [11][12]. In brief, we accessed through two databases: the Science Citation Index-Expanded (SCIE) database Core collection, from the Web of Science (WOS) platform Thomson Reuters and Pubmed database.
Concerning the WOS database, in the advanced search from WOS, we obtained the articles using this formula: TS=(Neurodegenerative disorders AND Africa) for the period 1975-2014. We verified each record to ensure its relevance. There were no restrictions regarding the document types. Then, we performed the "analysis results" function of WOS. We extracted: journals, most cited articles, authors, countries, funding agencies, organizations, publication years and Web of Science Categories. In order to evaluate the research networks between countries, after the analysis by country, we viewed the records of each country and then performed the analysis a second time in order to understand the links between the chosen country and the other countries. We then established the mapping diagram. To analyze the Web of Science Categories, we exported the date into a file "analyze.txt". This file can be read by the program wc10.exe. It generated map-files for VOSviewer [12][13][14]. These analyses were to compare with the same search but without "Africa". It means we performed the search TS=Neurodegenerative in WOS database. We added search of another database: Pubmed, to extend the results of the WOS database. We obtained publications using this formula: (Neurodegenerative disorders AND Africa) AND ("1900"(Date -Publication): "2014/12/31"(Date -Publication)). We extracted publication years. We extracted data with MEDLINE file. We then analyzed Medical Subject Headings (MeSH) with previously method described. We generated VOS-viewer picture as described [12][13][14].
The WOS core collection database and Pubmed database were used to perform our study. Publications from African countries could be not indexed in these databases.

Discussion
The results of our analysis of two databases present a majority of publications after 2006 (Table 1 and Table 2). Pubmed database allow us to say that studies on neurodegenerative disorders in Africa were performed decades ago [15]. Neurodegenerative disorders are therefore a burning issue for the African continent.
The increase of publications after 2006 is concordant with the general increase of publications in these two databases.
Nevertheless the general volume of publications is very low. In fact, only with the example of WOS database, 44 publications were found with the search "neurodegenerative disorders AND Africa" whereas we found more than 24000 publications with the search "Neurodegenerative disorders" without restraining to Africa. It represents only 0, 18% of the publications of this fields of research.
It means that the area studies are different if we restrain or not to Africa. According to Figure 2 and Figure 3, research in Africa appears to be focused on clinics. The goal is therefore to perform the diagnosis which seems under diagnosed [8; 16-17]. Moreover, different disease-specific hotspots can be determined.
To discuss these results, I will focus on the distinction between progressive and self-limiting disorders. Self-limiting neurological  [2]. Concerning Alzheimer's disease, it is due to amyloid plaques leading to dementia. As the first one, the aetiology and pathogenesis remain unclear, therefore management of patient is very difficult [3]. For the third one, Huntington's disease, it is There is no treatment [1]. For these examples of progressive neurological disorders, African countries propose the management of the patients [16][17]. It means that a structure is needed with physicians trained for diagnosis, predictive genetic testing in the case of some neurodegenerative disorders as Huntington's disease, What is known about this topic  Neurodegenerative disorders are involved in mortality and morbidity of every country;  High prevalence of neurodegenerative disorders is estimated in Africa;